This invention relates to an improved process for beet sugar production.
In a beet sugar factory using the calcium saccharate process, the sucrose contained in the beet juice is obtained as a product by purifying said beet juice in a purification step, then concentrating the purified beet juice, subjecting the concentrated beet juice to a plurality of stages of boiling and centrifugation thereby crystallizing sucrose, and finally recovering the sucrose crystals thus educed. The molasses resulting from the separation of sucrose from the massecuite is diluted and then mixed with quicklime to have the residual sucrose in the molasses combined with quicklime and produce a saccharate. The saccharate thus formed is separated in the form of a cake from the mother liquor. The separated saccharate cake is returned to the purification step, wherein it is treated in conjunction with the fresh beet juice, with the subsequent recovery of sucrose effected in the boiling and centrifugal separation step.
Generally the calcium saccharate process is practiced in a batchwise operation which comprises diluting the molasses to a sugar concentration (polarization) of 6%, cooling the diluted molasses to a temperature below 15.degree. C., agitating the molasses and simultaneously incorporating therein quicklime thereby causing precipitation of saccharate, and separating the saccharate formed from the mother liquor.
Recently, a continuous calcium saccharate process has been suggested by Raffinerie Tirlemontoise S.A. of Belgium to take the place of the batchwise calcium saccharate process described above. This continuous process comprises feeding and agitating molasses diluted to a sugar content (polarization) of 6 to 20%, and quicklime in a reactor provided with an agitator to produce calcium saccharate, forwarding the saccharate-containing solution to the subsequent step and, at the same time, withdrawing from the reactor the saccharate-containing solution in a volume three to ten times that of the molasses being delivered to the reactor, cooling the withdrawn solution and thereafter returning the cooled solution to the reactor in conjunction with the fresh supply of molasses and quicklime. Characteristic features of this continuous process include, for example, the fact that the molasses can be subjected to treatment in a concentration higher than that attainable in the batchwise process; the fact that the quicklime remaining unreacted can be utilized to advantage; as well as the fact that the treatment of molasses can be effected continuously. The saccharate produced achieves a remarkable growth, the particles measuring from 30 to 40 .mu.m as compared with only 1 to 2 .mu.m obtainable by the batchwise process. Consequently, the saccharate displays improved filterability. Accordingly, the saccharate cake obtained after the filtering and washing treatments has an enhanced true sucrose purity. Consequently, the impurities returned in conjunction with the saccharate cake to the purification step are proportionally lowered, with the result that the ratio at which sucrose is recovered in the boiling and centrifugal separation step is notably improved as compared with the batchwise process.
The beet juice, however, contains raffinose which impedes crystallization of sucrose. The raffinose is present at all times through the entire process of sucrose manufacture. During the step for the saccharate formation in the batchwise process and in the continuous process alike, the raffinose is combined with quicklime and precipitated. The resultant precipitate is entrained by the saccharate cake as it is recovered and circulated. Thus, the concentration of raffinose in the molasses gradually increases and eventually reaches a level at which the recovery of sucrose in the boiling and centrifugal separation step becomes infeasible from an economical point of view. Thus, it has heretofore been necessary to discharge the molasses out of the system after the raffinose content of the molasses has reached a certain level.
As techniques of sugar manufacture designed to decrease the amount of raffinose which accumulates in molasses and is circulated in the system, there have heretofore been suggested a process resorting to the use of strontium and a process relying on use of barium, for example. These methods have been only scarcely put into practice, however, because of factors, which are disadvantageous from an economical point of view.
Regarding the addition of quicklime to molasses wherein sucrose combines with lime and precipitates in the form of calcium saccharate, there has been proposed a process whereby the quicklime is added piecemeal and the precipitate produced by the addition of the first portion of quicklime, and therefore possessed of the highest raffinose concentration, is separated and withdrawn from the system. Using this process, however, it is difficult in practice to accomplish perfect separation and removal of raffinose alone, since sucrose is also precipitated in the form of a saccharate at the same time that raffinose is combined with the quicklime and consequently precipitated.
It is universally known that raffinose is hydrolyzed by .alpha.-galactosidase into sucrose and galactose. A method for commerical production of .alpha.-galactosidase by microorganisms, particularly fungi (molds) (U.S. Pat. Nos. 3,647,625, 3,832,284 and 3,867,256), has already been developed and is finding utility in the best sugar manufacturing industry.